For high data rate writer application, one of the requirements is to have fast saturation and low inductance to induce short rise time. On the other hand, a low fly height for high areal density recording beyond 60 GB is needed in order to have better head performance. Many reliability problems are, however, associated with this low fly height. Problems such as thermal pole tip protrusion induced by thermal mismatch between alumina and pole materials during the writing process will create a head-disk interface problem and eventually will damage the read head. One of the solutions to reducing thermal pole tip protrusion is to reduce DC coil resistance of the writer so that less heat is generated during the writing process. Additionally, lower DC coil resistance improves the coil's thermal reliability.
FIG. 1 is a schematic cross-section through a typical single coil planar design of the prior art. Seen in FIG. 1 are read head lower shield 11, read head upper shield 12, write head bottom pole 13 (P1), coil insulation 14, coil pedestal 15, write gap 16, coil housing lid 17, alumina-filled trench 18, write gap layer 19, coil 20, and top pole 23.
The main drawback of this structure is its high DC coil resistance. This is a result of the prior art processes used for its manufacture. In particular, because of the small size and internal spacings of the coil, the preferred material for enclosing and electrically isolating it has been hard baked photoresist. This material is well suited to filling in tiny openings and is soft enough to accommodate volume changes due to thermal expansion when operating at maximum power. Present processes used for planarizing a cavity filled with a coil and hard baked photoresist require that a significant amount of the thickness of the coils be removed. This, in turn, increases the DC resistance of a given coil having a given number of turns leading to a degradation of its performance.
In this invention, we describe a novel coil structure with low DC coil resistance for a short yoke length planar writer.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 6,490,131 (Sano et al) describes a device having dense windings of coil. The coil is elliptical in shape for low resistance and low heat generation. U.S. Pat. Nos. 6,385,009 and 6,262,867 (Sano et al) also disclose an elliptical coil with dense windings.